1. Field of the Invention
The present invention relates to an optical scanning device, an optical scanning method, a program, a recording medium, and an image forming apparatus. More specifically, the present invention relates to an optical scanning device, which scans a surface to be scanned with multiple light beams, an optical scanning method, a program used in the optical scanning device, a recording medium in which the program is recorded, and an image forming apparatus including the optical scanning device.
2. Description of Related Art
Image forming apparatuses using laser are widely mod in recording electrophotographic images. Each of the image forming apparatuses generally includes an optical scanning device and forms a latent image by rotating a photosensitive drum while scanning the drum with laser beam in the axis direction of the drum by using a polygon scanner (for example, a polygon mirror). In the field of electrophotography, the image forming apparatus requires high-image-density for improving an image quality, high operability and high speed to output an image for achieving an improvement in the processing speed.
For example, Japanese Patent Application Publication No. 2002-341273 discloses an optical scanning device in which multiple light beams are divided by optical deflection means using a rotating reflection surface, one portion of the divided beams scans an image carrier from a predetermined direction, and the other portion of the beams scans the image carrier from a direction opposite to the above-described direction. In the optical scanning device, the one portion and the other portion of the light beams all enter the rotating reflection surface of the optical deflector from a direction in which an entering angle to the rotating reflection surface of the optical deflector becomes larger with its rotation.
In addition, a method for scanning multiple lines with multiple light beams is disclosed (see, for example, Japanese Patent Application Publications No. 2003-211728 and No. 2004-100365).
Japanese Patent Application Publication No. 2003-211728 discloses an image forming apparatus including N optical scanning devices (N is a natural number equal to or larger than 2) and same-shaped housings. The N optical scanning devices form M scanning lines (M is larger than N(N<M) and is a natural number equal to or larger than 3) on a surface to be scanned. The M scanning lines include at least one scanning line which is not on the same plane. The same-shaped housings house the respective optical scanning devices. At least one of the optical scanning devices includes an optical system different from those included in the other optical scanning devices.
Japanese Patent Application Publication No. 2004-106365 discloses an image forming apparatus including a photoreceptor, a charging device, a multi-beam scanning device, a developing device and a transfer device. The charging device charges a surface of the photoreceptor. The multi-beam scanning device optically scans a surface to be scanned with multiple light beams generated by deflecting each of the light beams emitted respectively from multiple light sources, while the surface of the photoreceptor charged by the charging device is utilized as the surface to be scanned. The developing device supplies toner onto the surface of the photoreceptor which is optically scanned by the multi-beam scanning device. The transfer device transfers the toner supplied onto the surface of the photoreceptor by the developing device to a transfer body to be transferred. In the image forming apparatus, the superimposed length of the scanning lines formed on the surface to be scanned by the simultaneous optical scanning performed by the multi-beam scanning device is set to be equal to or less than a minimum pixel.
However, in the conventional image forming apparatuses as described above, a pixel formed of multiple dots cannot be accurately and stably formed. Thus, a high quality image cannot be formed at high speed. Furthermore, a high definition image quality has been recently demanded because image forming apparatuses have been also used for simple printing as on-demand printing systems.